On the Security of ID Based Signcryption Schemes

A signcryption scheme is secure only if it satisfies both the confidentiality and the unforgeability properties. All the ID based signcryption schemes presented in the standard model till now do not have either the confidentiality or the unforgeability or both of these properties. Cryptanalysis of some of the schemes have been proposed already. In this paper, they present the security attack on 'Secure ID based signcryption in the standard model' proposed by Li-Takagi and flaws in the proof of security of 'Efficient ID based signcryption in the standard model' proposed by Li et al., which are the recently proposed ID based signcryption schemes in the standard model.